53 research outputs found
Dielectric geometric phase optical elements from femtosecond direct laser writing
We propose to use femtosecond direct laser writing technique to realize
dielectric optical elements from photo-resist materials for the generation of
structured light from purely geometrical phase transformations. This is
illustrated by the fabrication and characterization of spin-to-orbital optical
angular momentum couplers generating optical vortices of topological charge
from 1 to 20. In addition, the technique is scalable and allows obtaining
microscopic to macroscopic flat optics. These results thus demonstrate that
direct 3D photopolymerization technology qualifies for the realization of
spin-controlled geometric phase optical elements.Comment: 6 figure
A New Look at Calcium Digermanide CaGe: A High-Performing Semimetal Transparent Conducting Material for Ge Optoelectronics
Following a recently manifested guide of how to team up infrared transparency
and high electrical conductivity within semimetal materials [C. Cui
Prog. Mater. Sci. 2023, 136, 101112], we evaluate an applicability of the
calcium digermanide (CaGe) thin film electrodes for the advanced Ge-based
optical devices. Rigorous growth experiments were conducted to define the
optimal annealing treatment and thickness of the Ca-Ge mixture for producing
stable CaGe layers with high figure of merit (FOM) as transparent
conducting material. Ab-initio electronic band structure calculations and
optical modeling confirmed CaGe semimetal nature, which is responsible for
a demonstrated high FOM. To test CaGe electrodes under actual conditions, a
planar Ge photodetector (PD) with metal-semiconductor-metal structure was
fabricated, where CaGe/Ge interface acts as Schottky barrier. The resulting
Ge PD with semimetal electrodes outperformed commercially available Ge devices
in terms of both photoresponse magnitude and operated spectral range. Moreover,
by using femtosecond-laser projection lithography, a mesh CaGe electrode
with the relative broadband transmittance of 90\% and sheet resistance of 20
/sq. was demonstrated, which further enhanced Ge PD photoresponse.
Thus, obtained results suggest that CaGe thin films have a great potential
in numerous applications promoting the era of advanced Ge optoelectronics.Comment: 12 pages, 4 figure
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